The Humern empire is vast, unbelievably powerful and (in certain matters) brutally authoritarian.

One such issue is that of reproduction. In order to ensure that all subjects of the Empire remain part of the same species all breeding must be done either by taking a randomly chosen fertilised egg from a Reproduction Center (random in that the egg is picked randomly from a bank of egg/sperm pairings carefully chosen to ensure forward and backward genetic compatibility) or by having the genes of yourself and your partner analysed to ensure you have a reasonable chance of producing compatible offspring (knowing your offspring may well be ‘incompatible’ and this never have children of their own).

Unless a subject goes down one of these two routes they are sterile. They are born sterile, live sterile and can only have sterility taken away at the discretion of the Empire. This is to prevent any breakaway faction or splinter groups being able to reproduce and split into a whole new species (and certainly not so the Empire has an iron grip on the family jewels of all of it’s colonies)

The question is how can such reversible sterility be woven into (for arguments sake) the human genetic code? It is still required that eggs and sperm be available to fill the Reproduction Centers, but the sterility must be status quo without intervention (ie removal of all eggs at birth is not an option as a rebel government might choose to stop doing it)

Answers will be ranked by how biologically complex the changes are, how hard the ‘reversal’ is without proper authorisation, and how low the chance of pregnancy becomes (because it will never be bang on 0, but rebels shouldn’t be able to breed without insane levels of luck).

Details on the biological cause of the sterility are required, even if they’re just an overview. More detail is, in my view, a better answer, but I understand the complexity here (I’m not asking for which proteins need editing, just methods by which this kind of sterility could be effected).

Bonus points: if the changes can be applied to an otherwise healthy human population by means of a retrovirus. Not that the subjects of the Empire won’t willingly submit to such a draconian measure, you understand...

  • $\begingroup$ What is the expected scope of an answer? Do you need molecular biological specifics down to the gene you want to modify or are you just interested in a basic description of how genetic engineering works in general? Perhaps you are unaware of how complex this is, getting a quantitative chance for pregnancy is way, way, way beyond what I would expect from an answer. You are potentially asking a lot here, I think you need to set some sort of quality criteria for answers and be absolutely clear on what an answer needs to actually answer $\endgroup$ – Raditz_35 Sep 25 '18 at 8:19
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    $\begingroup$ @Raditz_35 I’ve added a paragraph on scoping. When it comes to chance of pregnancy exact chances aren’t required, but ‘no males produce sperm without supplementary hormones’ would seem to have a lower chance of accidental pregnancy than ‘Fallopian tubes are malformed at birth and need corrective surgery’ $\endgroup$ – Joe Bloggs Sep 25 '18 at 8:27
  • $\begingroup$ I wrote my answer before your edit. does it fit it, or not? $\endgroup$ – L.Dutch - Reinstate Monica Sep 25 '18 at 8:28
  • $\begingroup$ @L.Dutch It does, though if anyone can point out which proteins would be good to turn off it’d be better. :-) $\endgroup$ – Joe Bloggs Sep 25 '18 at 8:31

You could give your population Mild Androgen Insensitivity Syndrome and in particular the variant that reduces (but does not block) the transcription of the androgen receptor. This is done by engineering a retrovirus that increases the length of the polyglutamine tract on exon 1 of the Xq11-Xq12 locus on the X chromosome (Genetics of AIS). Do not increase it overmuch or you will cause disease in your male population, too little will not cause the effect you are after: male infertility due to lack of spermatogenesis (no sperm cells). Your females are all normal in every way except that they carry a copy of the defective gene on both X chromosomes. You may need to experiment a bit to find a length between 21 and 40 CAG repeats that gives the desired effect without too many nasty side effects (such as osteoporosis or male breast development or incomplete male genitalia and many others).

In your reproduction clinic you will only select females which carry the defective gene on both X-chromosomes. To make the males fertile give them excess testosterone. You cannot do this long and it needs to be monitored for adverse health effects as liver disease, prostate cancer, breast cancer, to name a few. Screen for mutations in both the parents as well as the offspring as this sequence is quite mutation prone.

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    $\begingroup$ This answer dederves a bounty, +1. $\endgroup$ – The Square-Cube Law Sep 25 '18 at 11:18
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    $\begingroup$ Ok! Exceptionally useful answer there, with enough supplementary information that I can get lost down a rabbit hole working out potential side effects/fixes for side effects. +1 $\endgroup$ – Joe Bloggs Sep 25 '18 at 14:41

You want to prevent reproduction, not intercourse. For that you just need to cripple one of the two sexes.

For example you can damage (remove) one of the many proteins needed to have a sperm/egg cell able to fulfill its task. I.e. you could suppress the tail formation for the sperm cells, or the egg nesting ability in the female body.

For those who are allowed to reproduce, you will host them in dedicated centers, where they will be provided "reproductionally enriched food and water", where the missing proteins, that you know, is supplied in their diet.

However, this won't protect you from casual mutations, so you have to perform routine checks and updates.

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    $\begingroup$ The issue is that the suppression of reproduction cannot rely on something being done by ‘the government’, it has to be the ground state, so coding the lack of a protein is better than suppressing the creation of the protein. Good point about casual mutations though... $\endgroup$ – Joe Bloggs Sep 25 '18 at 8:30
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    $\begingroup$ @JoeBloggs, edited to fit your specs (I hope) $\endgroup$ – L.Dutch - Reinstate Monica Sep 25 '18 at 8:35

Vasectomies are reversible

But you want something woven into the human's 'base code'. So you genetic engineer the vas deferns either to be too small to pass sperm, to not be connected, or to not exist at all.

This is simpler than some sort of protein change that could have other, far-reaching implications of biochemistry, and it isn't a disease that could accidentally cripple one or the other sex. This is just a part that isn't there, but isn't needed for anything else.

If you want to reverse the sterility, you put a plastic tube in there. If we you want to re-reverse the sterility, you take the tube out.

Of course, it doesn't really sound like you want sex by intercourse at all; if you are going to be just breeding people in fertility centers or whatever, then you just extract sperm from the males you want to reproduce, no vas deferns needed at all.


Don't have males born into the general populace.

They store semen in giant freezers, sometimes they allow a male embryo to be born in a lab or the ruling family, who has their external genitalia surgically corrected into female-norm because in their society, anything else would be abnormal but can still produce sperm in a way to replenish your frozen stocks.

As to two people being able to produce offspring if they are "genetically superior" - you either need to the technology to make an embryo out of two ova or lie to them and say the child is theirs.

  • $\begingroup$ Well, it's entirely possible to strip out the genetic material in a sperm and replace it with other genetic material, so female/female genetic pairings could still be possible. When it comes to only letting females be born are you suggesting editing the genetic code so only females can be born without intervention? $\endgroup$ – Joe Bloggs Sep 25 '18 at 9:25
  • $\begingroup$ @JoeBloggs you don't really need to edit the genetic code, do you? In humans Y chromosomes are only found in males, so if you don't keep any of them around, you cannot combine the chromosomes found in two ova and get a male baby. If you do keep some male specimens then it is just a question of screening the sperm you use in your reproduction clinics so none contain a Y chromosome. And it would become reversible when someone found a forgotten stash of frozen sperm containing Y chromosomes. $\endgroup$ – Real Subtle Sep 26 '18 at 6:16
  • $\begingroup$ good point. As long as the males and Y sperm are highly regulated by the Empire this could work. $\endgroup$ – Joe Bloggs Sep 26 '18 at 12:17

Biological systems are always going to be messy and imprecise. Whatever method you choose to enforce sterility there are likely to be some exceptions that will manage to procreate. As a wise man once said, “Life, uh, finds a way”. With this understanding, it should be clear that enforcing sterility in women is much more important than doing so in men. Imagine what would happen if a rogue government manages to find one fertile male on their planet and all of the females are already fully fertile? One female escaping sterility does not represent nearly as much of a threat. Of course, the strongest barrier would be sterility in both men and women requiring two individuals to overcome their sterility and find each other which would be a much rarer occurrence.

All that said, in order to make sterile humans we don’t need to rely on existing human disorders which are necessarily imprecise and will have many side effects. There are many genes that are used in the reproductive system that are not used anywhere else in the body. All you have to do is knockout an essential gene, of which there are sure to be dozens if not hundreds of candidates, and you have complete infertility with no side effects. The only question is where to break the system to achieve the most complete infertility, the fewest undesirable side effects, and the easiest reversibility.

For males, the simplest change is disabling a gene directly required for the functioning of mature sperm. This could mean sabotaging the acrosome, the flagellum, protamines, really any gene unique to the sperm can be broken without any effect on the rest of the organism. This would result in complete male infertility reversible only by genetic engineering.

For females, the analogous simplest change could be breaking egg-specific genes and processes which would do fine, but an alternative would be preventing menstruation entirely. The menstrual cycle is regulated by various hormonal clocks. We can already manipulate this process with ingested chemicals so it would be relatively straightforward to genetically turn off the menstrual cycle entirely. This has the advantage of eliminating the general unpleasant burden of menstruation from the female population but also allows for easy reversibility with orally ingested hormones being sufficient to start egg maturation again.


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